The present invention relates to a method of manufacturing brush heads.
The invention is particularly, but not exclusively, applicable to brush heads such as for paint brushes and other brushes used in decorating.
Conventional brushes comprise a handle and a head which has a ferrule attached to the handle and a knot of natural or synthetic bristles or filaments (hereinafter referred to as xe2x80x9cbristlesxe2x80x9d), the basal end portion of which is embedded in hardened epoxy resin, which retains the basal end portion of the knot of bristles in the ferrule, the remainder of the knot of bristles protruding from the ferrule.
In manufacture of such a brush head, the end portion of the knot of bristles is located in the ferrule and then is impregnated with uncured (liquid) epoxy resin (incorporating hardener or curing agent), which hardens or cures. It is necessary that the basal end portion of the knot of bristles is gripped by the ferrule until the resin has hardened or cured, in order to prevent or reduce loss of bristles from the bush head.
In order to enhance the gripping of the bristles by the ferrule one or more wedges (which may be up to nine in number) may be located in the ferrule.
When one or more wedges are used, the knot of bristles is inserted, tip end first, into the ferrule, then the wedge is or the wedges are inserted into the knot at the basal end of the knot, and then the knot is moved relative to the ferrule (this step is referred to as xe2x80x9cpull upxe2x80x9d) to its desired final position relative to the ferrule, to leave a cavity between one end of the ferrule and the basal end of the knot, the bristles projecting from the other end of the ferrule. The resin is then introduced into the cavity.
Conventionally the wedges are made of balsa, plywood, cardboard or hard plastics material. When the wedges are of cardboard the number required varies from two up to nine. The wedges are simple fed into the knot of bristles in the ferrule and are static, i.e. they do not fill any void left between the bristles and the inside surface of the ferrule.
The knot of bristles is picked by cross section but because of variations in bristle weight and density the volume of bristle located in the ferrule varies from ferrule to ferrule. If the volume is too low the wedges will not fill voids left between the bristles and the inside surface of the ferrule to ensure a tight fit of the bristles in the ferrule and the knot may accordingly be too loosely held in the ferrule. If the volume is too high the bristle may accordingly be too tightly held in the ferrule. As a result, if the bristles are too loosely held in the ferrule, before the resin has been impregnated into the basal end portion of the bristles and the resin has cured, bristles may fall out of the ferrule or the knot may slide or drop from its desired position relative to the ferrule, or if the knot is too tightly held in the ferrule the sides of the ferrule may bow outwardly, thereby preventing or hindering the subsequent location of an end of the handle in the ferrule. Consequently wastage occurs because unsatisfactory brush heads have to be rejected and down-time of the brush head manufacturing equipment arises for adjustment to be made to the cross-section of bristle picked for each knot or the number of wedges used in each brush head.
The present invention aims, at least in its preferred embodiments, to overcome the aforementioned disadvantages.
In accordance with the present invention there is provided a method of manufacturing a brush head, comprising: locating in a ferrule the basal end portion of a knot of bristles; compressing at least one wedge of resiliently deformable material by an amount such that the wedge or wedges remains capable of recovering to its or their original size and shape; before the wedge or wedges have recovered to their original size and shape, inserting them into the basal end portion of the knot of bristles in the ferrule; the wedge or wedges, as it or they recover compressing the bristles against an inside surface of the ferrule to enhance retention of the bristles by the ferrule; impregnating the basal end portion of the knot of bristles with liquid resin; and thereafter allowing or causing the resin to harden to retain the basal end portion of the knot of bristles in the ferrule.
The compression of the wedge or wedges, prior to its or their being inserted into the ferrule, may be effected by squeezing the wedge or wedges through a set of rollers.
Preferably the wedge or wedges are compressed in a direction transverse to the direction in which they are to be inserted into the knot of bristles. Preferably the wedge or wedges are elongate and the direction in which each is compressed is its thickness direction, transverse to its length.
Preferably the or each wedge is compressed by an amount such as to reduce its linear dimension in the direction of compression by at least 5%, more preferably 15%.
Preferably the wedge or wedges are inserted at the basal ends of the bristles with the bristles located in an initial position in the ferrule and then pull up is effected to bring the knot to its desired final position relative to the ferrule.
Preferably, the amount of bristle located in the ferrule is such that the linear dimension of the wedge or wedges in the direction of compression is prevented from recovering to more than 95% of its original value, although a satisfactory brush head is obtained if all voids in the ferrule are filled when the linear dimension of the wedge or each wedge in the direction of compression has recovered to 100% of its original value.
The wedge may be of a microcellular polymer, e.g. polyvinylchloride (PVC).
Since the wedge or wedges recover any deficiency in the volume of the basal end portion of the bristles located in the ferrule is accommodated. Even if the volume of the basal end portion of the bristles is high, although the recovery of the wedge or wedges will be restricted there is only a small risk of the sides of the ferrule bowing. Thus the problem of reject heads is substantially removed, thereby reducing wastage of brush heads and down-time of the brush head manufacturing equipment.
The bristles are held in the. ferrule under a pressure exerted by the wedges such as to allow even penetration of the resin. This also prevents the bristles dropping out of the ferrule during storage, transport or other processing prior to resin setting (hardening or curing) and therefore reduces rejects at the head finishing stage.
Normally no more than two wedges are required in each brush head.
It will be understood by those skilled in the art that the wedges used need not be of tapering section.